Adjusting Tilted Sprinkler Heads

My system was installed about a year ago, but about 9 or 10 of the heads are starting to severely tilt in the hard, clay soil. As a result, I'm starting to develop brown spots from uneven coverage. Question: what is the best method for straightening the heads and keeping them straight? Is it just a matter of digging down to the pvc and placing rocks and soil around the stems, or is there some other recommendation? Thanks for your help.

REally the best way to get them good and straight is, like you said, dig up the head. If the sprinklers were installed correctly, they should have a foot or so of flexible black pipe (funny pipe) between the rigid pvc and the head. This allows you to easily straigten, raise, or lower each head as needed. You probably won't even need to dig to the bottom of the head, but if you don't, be sure not to force anything too hard. When I have the head loose, I like to hold the head straight and at the correct level with one of my feet standing on top. I then backfill with my shovel. Use something ( a packing bar or end of a 2x4, etc) to tamp the soil around the head. But keep your foot on top of the head, or it will move out of plumb with each tamp. Good luck.